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Abstract:

In regard to a second direction (combination direction) that is turned
back by a reflection at the time of light-guiding, a projective optical
system has an emission opening width larger than an opening width of a
third reflective surface, such that it is possible to prevent a partial
deficiency of image light when the image light emitted from the
projective optical system is incident to the third reflective surface
from occurring, and thereby it is possible to prevent the occurrence of
deficiency of an image or a large variation in brightness.

Claims:

1. A virtual image display device, comprising: an image display device
that emits image light; a projective optical system that allows the image
light emitted from the image display device to be incident; and a light
guiding member, comprising: a light guiding portion; a light incidence
portion that allows the image light to be incident to the light guiding
portion; and a light emission portion that emits the image light guided
by the light guiding portion to the outside, and that makes the image
light visible through the light emission portion, the light guiding
portion having a first reflective surface and a second reflective surface
that are disposed in parallel with each other and allow the image light
to be guided through a substantially total reflection, the light
incidence portion having a third reflective surface that defines an
opening width and makes a predetermined angle with respect to the first
reflective surface, the light emission portion having a fourth reflective
surface that makes a predetermined angle with respect to the first
reflective surface, and the projective optical system having an emission
opening width that is larger than the opening width of the third
reflective surface in a direction that is parallel with a plane of the
first reflective surface and is orthogonal to an intersection line
between the first reflective surface and the third reflective surface.

2. The virtual image display device according to claim 1, a distance from
a lens, which is closest to the light emission side, of the projective
optical system to the first reflective surface of the light guiding
member being 3 mm or less.

3. The virtual image display device according to claim 1, the emission
opening width of the projective optical system in a second direction that
is parallel with the first reflective surface and is orthogonal to the
intersection line between the first reflective surface and the third
reflective surface being smaller than that in a first direction that is
parallel with the intersection line between the first reflective surface
and the third reflective surface.

4. The virtual image display device according to claim 3, an effective
size of the image display device in the second direction being larger
than that in the first direction.

5. The virtual image display device according to claim 1, the number of
times of reflection of a first image light beam emitted from a first
partial region in the image display device in the light guiding portion,
and the number of times of reflection of a second image light beam
emitted from a second partial region different from the first partial
region in regard to a confinement direction in which a return of an
optical path due to reflection occurs at the time of the light-guiding,
in the light guiding portion, being different from each other.

6. The virtual image display device according to claim 5, the confinement
direction being a direction that is parallel with a cross-section
including a first optical axis passing through the projective optical
system and a normal line of the third reflective surface.

7. The virtual image display device according to claim 1, further
comprising: a wedge-shaped light transmitting member that has having a
transmissive surface that is opposite to the fourth reflective surface;
and a half mirror formed on the fourth reflective surface.

8. The virtual image display device according to claim 7, the
wedge-shaped light transmitting member further comprising a first surface
and a second surface that are disposed in parallel with the first
reflective surface and the second reflective surface, respectively.

9. The virtual image display device according to claim 1, the light
guiding member being integrally molded independently by injection
molding.

10. The virtual image display device according to claim 9, the light
guiding member being molded from a thermal polymerization type resin
material.

11. A virtual image display device, comprising: an image display device
that emits image light; a projective optical system that converts the
image light into a parallel light beam; and a light guiding member having
a light guiding portion and a light emission portion, the light guiding
portion having a plurality of reflective surfaces forming a polyhedral
shape with at least two corners that form end surfaces, the plurality of
reflecting surfaces reflecting the parallel light beam, at least one of
the plurality of reflective surfaces defining an open end width, and the
projective optical system defining an emission opening width that is
larger than the opening width of the at least one of the plurality of
reflective surfaces.

12. The virtual image display device according to claim 11, at least
another of the plurality of reflective surfaces having a plurality of
layers.

13. A method of forming a virtual image, the method comprising: emitting
a two-dimensional illumination light with an illumination device housed
in an image display device; spatially modulating the illumination light
to form an image light; outputting an image signal to a liquid crystal
display device to form a colored-image light; emitting the colored-image
light through a projective optical system that converts the colored-image
light into a parallel light beam, the projective optical system having an
emission opening width that is larger than an opening width of a third
reflective surface in a direction that is parallel with a plane of a
first reflective surface and is orthogonal to an intersection line
between the first reflective surface and the third reflective surface;
passing the light beam through a light incidence portion having the third
reflective surface that makes a predetermined angle with respect to the
first reflective surface; passing the light beam into a light guiding
portion having the first reflective surface and also having a second
reflective surface, the first and second reflective surfaces being
disposed in parallel with each other, allowing the image light to be
guided through a substantially total reflection; reflecting the light
beam by a plurality of reflective surfaces in the light guiding portion;
and emitting the light beam that is incident to an observer's eye from a
light emission portion of the light guiding portion guided by the light
guiding member to the outside, the light emission portion having a fourth
reflective surface that makes a predetermined angle with respect to the
first reflective surface.

14. The method claim 13, wherein the image light passes through at least
three lenses of the projective optical system.

15. A virtual image display device that forms a virtual image according
to the method of claim 13.

Description:

[0001] This Application claims priority to JP 2011-022445 filed in Japan
on Feb. 4, 2011, the entire disclosure of which is herein incorporated by
reference in its entirety.

BACKGROUND

[0002] 1. Technical Field

[0003] The present invention relates to a virtual image display device
such as a head-mounted display that is used by being mounted on the head.

[0004] 2. Related Art

[0005] In recent years, as a virtual image display device that allows a
virtual image to be formed and to be observed similarly to the
head-mounted display, various virtual image display devices of a type in
which image light from a display element is guided to a pupil of an
observer by a light guiding plate have been suggested.

[0006] In this virtual image display device, the image light and external
light overlap each other, such that a see-through optical system has been
suggested (refer to JP-A-2006-3879 and JP-A-2010-224473).

[0007] However, in the device disclosed in JP-A-2006-3879 or the like, the
see-through state is realized by a pupil division method that uses a
light guiding optical system in which an emission opening is smaller than
a pupil size, such that it is difficult to make a display size of the
virtual image large. In addition, the light guiding optical system that
is smaller than the size of the pupil is used, such that it is difficult
to make an effective pupil diameter (a lighting diameter that allows the
virtual image to be taken in, and is called an Eyring diameter) large so
as to correspond to an individual pupil width in humans. In addition, the
emission opening or a casing of the light guiding optical system is
physically disposed in the vicinity of the pupil, such that a blind spot
is generated, and therefore it is not necessarily perfectly see-through.

[0008] In addition, as an optical system for the head-mounted display, an
optical system including a light guiding pipe that allows a plurality of
light modes in which the light guiding angles are different from each
other to progress (refer to JP-A-2008-535001) is disclosed. In this
optical system, it may be considered that a third optical surface at an
emission side is set as a half mirror, and light that is transmitted
through the third optical surface is made to go straight to realize a
see-through type display device.

[0009] However, in the optical system disclosed in JP-A-2008-535001, a
liquid crystal panel is illuminated with collimated light in which a
different angle of incidence is set for each of the optical modes on the
assumption that a phase of each of the plurality of optical modes is
misaligned. In addition, display content is changed by each optical mode,
and a display of each optical mode is sequentially performed, and thereby
an image of each optical mode is connected to obtain an entire image. In
this case, it is necessary to display a center image and left and right
images, which make up the entire image while they are changed at a time
interval by one liquid crystal panel, such that a virtual image display
device becomes complex and an observed image becomes dark.

[0010] Separately from this configuration, it may be considered that in a
virtual image display device that allows a virtual image to be observed
in an overlapped manner with external light due to a light guiding member
provided with a light emitting portion to cover the front of an eye, it
is not necessary to connect an image at a time interval. However, it is
not easy to display a large image, and a deficiency of the image or a
variation in brightness is apt to occur in the horizontal light guiding
direction.

SUMMARY

[0011] An advantage of some aspects of the invention is to provide a
virtual image display device that can display a virtual image of a high
quality by suppressing a deficiency of an image or a variation in
brightness.

[0012] An aspect of the invention is directed to a virtual image display
device including (a) an image display device that forms image light; (b)
a projective optical system that allows the image light emitted from the
image display device to be incident; and (c) a light guiding member that
includes a light guiding portion, a light incidence portion that allows
the image light to be incident to the light guiding portion, and a light
emission portion that emits the image light guided by the light guiding
portion to the outside, and makes the image light visible through the
light emission portion, in which (d) the light guiding portion has a
first reflective surface and a second reflective surface that are
disposed in parallel with each other and allow the image light to be
guided through a total reflection, (e) the light incidence portion has a
third reflective surface that makes a predetermined angle with respect to
the first reflective surface, (f) the light emission portion has a fourth
reflective surface that makes a predetermined angle with respect to the
first reflective surface, and (g) the projective optical system has an
emission opening width that is larger than an opening width of the third
reflective surface in a direction that is parallel with a plane of the
first reflective surface and is orthogonal to an intersection line
between the first reflective surface and the third reflective surface.

[0013] According to the virtual image display device, in regard to a
combination direction that is turned back by a reflection at the time of
light-guiding, the projective optical system has the emission opening
width larger than the opening width of the third reflective surface, such
that it is possible to prevent a partial deficiency of image light when
the image light emitted from the projective optical system is incident to
the third reflective surface from occurring, and thereby it is possible
to prevent the occurrence of deficiency of an image or a large variation
in brightness.

[0014] In a specific aspect of the invention, the virtual image display
device may be configured such that a distance from a lens, which is
closest to the light emission side, of the projective optical system, to
the first reflective surface of the light guiding member is, for example,
3 mm or less. In this case, it is possible to efficiently make the image
light, emitted from the lens which is closest to the light emission side
of the projective optical system, incident to the second reflective
surface through the first reflective surface.

[0015] In another aspect of the invention, the virtual image display
device may be configured such that the emission opening width of the
projective optical system in a second direction that is parallel with the
first reflective surface and is orthogonal to the intersection line
between the first reflective surface and the third reflective surface is
smaller than that in a first direction that is parallel with the
intersection line between the first reflective surface and the third
reflective surface.

[0016] In another aspect of the invention, the virtual image display
device may be configured such that an effective size of the image display
device in the second direction is larger than that in the first
direction.

[0017] In another aspect of the invention, the virtual image display
device may be configured such that the number of times of reflection of
first image light beam, which is emitted from a first partial region in
the image display device, in the light guiding portion, and the number of
times of reflection of second image light beam, which is emitted from a
second partial region different from the first partial region in regard
to a confinement direction in which a return of the optical path due to
reflection occurs at the time of light-guiding, in the light guiding
portion are different from each other. In this case, image light beams in
which the numbers of times of reflection are different from each other
are used, such that it is possible to make an angle of emission of the
image light emitted from the light emission portion have a wide angle
width. That is, it is possible to take in image light from different
partial regions in an image display device at a relatively wide angle of
view, such that it is possible to secure a large display size in a
virtual image that is observed over the light emission portion. In this
way, due to the setting of a structure in which image light beams in
which the numbers of times of reflection are different from each other
are taken out, it is possible to make the light emission portion large so
as to cover a pupil without making the light guiding portion too much
thicker. In addition, the above-described confinement direction
represents a direction that is orthogonal to a plane of the first
reflective surface and is orthogonal to the intersection line between the
first reflective surface and the third reflective surface in the
plate-shaped light guiding portion. In addition, the confinement
direction corresponds to a direction that is parallel with the plane of
the first reflective surface and is orthogonal to the intersection line
between the first reflective surface and the third reflective surface, at
an upstream side in an optical path in relation to the light incidence
portion, that is, in the projective optical system or the like.

[0018] In another aspect of the invention, the virtual image display
device may be configured such that the confinement direction is a
direction that is parallel with a cross-section including a first optical
axis passing through the projective optical system and a normal line of
the third reflective surface. In the image light beams from different
positions in regard to the cross-sectional direction, angles of emission,
that is, angles of incidence to the light incidence portion are made to
be different from each other, such that it is possible to make the
numbers of times of reflection in the light guiding portion different.

[0019] In another aspect of the invention, the virtual image display
device may further include a wedge-shaped light transmitting member that
has a transmissive surface that is opposite to the fourth reflective
surface, and a half mirror may be formed on the fourth reflective
surface. According to this configuration, it is possible to guide
external light to a pupil through the fourth reflective surface and the
light transmitting member, and thereby natural observation of the outside
may be realized.

[0020] In another aspect of the invention, the virtual image display
device may be configured such that the light transmitting member has a
first surface and a second surface that are disposed in parallel with the
first reflective surface and the second reflective surface, respectively.
According to this configuration, a see-through observation by the light
transmitting member may be performed without distortion and with a high
degree of flatness.

[0021] In another aspect of the invention, the virtual image display
device may be configured such that the light guiding member is integrally
molded independently through an injection molding. In this case, it is
possible to produce the light guiding member and the light transmitting
member with high accuracy using an injection molding technique.

[0022] In another aspect of the invention, the virtual image display
device may be configured such that the light guiding member is molded
from a thermal polymerization type resin material. In this case, it is
possible to increase weight reduction and safety due to the resin, and
thereby a stable and highly accurate molding due to thermosetting may be
realized.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The invention will be described with reference to the accompanying
drawings, wherein like numbers reference like elements.

[0024]FIG. 1 is a perspective view illustrating a virtual image display
device of an embodiment;

[0025]FIG. 2A is a plan view of a main body portion of a first display
device making up the virtual image display device, and FIG. 2B is a front
elevation view of the main body portion;

[0026]FIG. 3 is a perspective view illustrating the main body portion of
the first display device;

[0027]FIG. 4A is a diagram illustrating a structure of a third reflective
surface in a light incidence portion of a light guiding member, FIG. 4B
is a diagram illustrating a structure of a first reflective surface in a
light guiding portion of the light guiding member, FIG. 4c is a diagram
illustrating a structure of a second reflective surface in the light
guiding portion, and FIG. 4D is a diagram illustrating a structure of a
fourth reflective surface in a light emission portion;

[0028]FIG. 5A is a conception diagram in which an optical path in
relation to a first vertical direction is developed, and FIG. 5B is a
conception diagram in which an optical path in relation to a second
horizontal direction is developed;

[0029]FIG. 6 is a plan view specifically illustrating an optical path in
an optical system of a virtual image display device;

[0030]FIG. 7A is a diagram illustrating a display surface of a liquid
crystal display device, FIG. 7B is a diagram conceptionally illustrating
a virtual image of the liquid crystal display device, which is viewed by
an observer, and FIGS. 7C and 7D are diagrams illustrating two partial
images making up the virtual image;

[0031]FIG. 8 is a plan view specifically illustrating a separate optical
path in the optical system of the virtual image display device;

[0032]FIG. 9A is a diagram illustrating the reason why an end surface
formed by removing a corner is provided to the light guiding member, and
FIG. 913 is a diagram illustrating the reason why a separate end surface
is provided to the light guiding member; and

[0033]FIG. 10A is a diagram illustrating a light guiding state of image
light in a modification, and FIG. 10B is a diagram conceptionally
illustrating a virtual image of a liquid crystal display device in the
modification.

DETAILED DESCRIPTION OF EMBODIMENTS

[0034] Hereinafter, a virtual image display device related to an
embodiment of the invention will be described in detail with reference to
the accompanying drawings.

A. External Appearance of Virtual Image Display Device

[0035] A virtual image display device 100 of an embodiment illustrated in
FIG. 1 is a head-mounted display having the same external appearance as
eyeglasses, and allows an observer wearing this virtual image display
device 100 to perceive image light via a virtual image and allows the
observer to observe an external image in a see-through manner. The
virtual image display device 100 includes an optical panel 110 that
covers the front of the observer's eyes, a frame 121 that maintains the
optical panel 110, and first and second driving portions 131 and 132 that
are provided at a portion ranging from end-piece to temple of the frame
121. Here, the optical panel 110 includes a first panel portion 111 and a
second panel portion 112, and both panel portions 111 and 112 are formed
of a plate-shaped part and are integrally connected at the center of the
optical panel 110. A first display device 100A including the first panel
portion 111 and the first driving portion 131 at the left-side in the
drawing is a portion that forms a left-eye virtual image, and also
functions independently as a virtual image display device. In addition, a
second display device 100B including the second panel portion 112 and the
second driving portion 132 at the right-side in the drawing is a portion
that forms a right-eye virtual image, and also functions independently as
a virtual image display device. In addition, the first and second driving
portions 131 and 132 are individually accommodated in a light-shielding
and protective casing 141.

B. Structure of Display Device

[0036] As shown in FIG. 2A or the like, the first display device 100A
includes an image forming device 10 and a light guiding device 20. Here,
the image forming device 10 corresponds to the first driving portion 131
in FIG. 1, and the light guiding device 20 corresponds to the first panel
portion 111 in FIG. 1. In regard to the image forming device 10, a main
body portion excluding the casing 141 shown in FIG. 1 is shown. In FIG.
2A, a portion of the light guiding device 20 is shown by a
cross-sectional view taken along an arrow A-A in FIG. 2B. In addition,
the second display device 100B shown in FIG. 1 has the same structure as
the first display device 100A except that the left and right are
reversed, such that the detailed description of the second display device
100B will not be repeated.

[0037] The image forming device 10 includes an image display device 11 and
a projective optical system 12. The image display device 11 includes an
illumination device 31 that emits two-dimensional illumination light SL,
a liquid crystal display device 32 that is a transmission-type spatial
optical modulation device, and a driving control unit 34 that controls an
operation of the illumination device 31 and the liquid crystal display
device 32.

[0038] The illumination device 31 includes a light source 31a that
generates light including three colors of red, green, and blue, and a
backlight light-guiding portion 31b that diffuses the light from the
light source 31a and converts this light into a light beam having a
rectangular cross-section. The liquid crystal display device 32 spatially
modulates illumination light SL emitted from the illumination device 31
and forms image light, which is an object to be displayed, such as a
moving picture. The driving control unit 34 includes a light source
driving circuit 34a and a liquid crystal driving circuit 34b. The light
source driving circuit 34a supplies power to the light source 31a of the
illumination device 31 and allows the illumination light SL with a stable
brightness to be emitted. The liquid crystal driving circuit 34b outputs
an image signal or a driving signal to the liquid crystal display device
32, and forms colored-image light that becomes an origin of the moving
picture or a still image as a transmittance pattern. In addition, the
liquid crystal driving circuit 34b may be provided with an image
processing function, but the image processing function may be provided to
a control circuit that is externally provided. The projective optical
system 12 is a collimated lens that converts image light emitted from
each point on the liquid crystal display device 32 into a parallel light
beam.

[0039] In the liquid crystal display device 32, a first direction D1
corresponds to an extension direction of a vertical cross-section
including a first optical axis AX1 passing through the projective optical
system 12 and a specific line parallel with a third reflective surface
21c of the light guiding member 21, which is described later, and a
second direction D2 corresponds to an extension direction of a horizontal
cross-section including the first optical axis AX1 and a normal line of
the third reflective surface 21c. In other words, the first direction D1
is a direction parallel with an intersection line between a first
reflective surface 21a of the light guiding member 21, which is described
later, and the third reflective surface 21c, and the second direction D2
is a direction parallel with a plane of the first reflective surface 21a
and is orthogonal to the intersection line between the first reflective
surface 21a and the third reflective surface 21c. That is, in regard to a
position of the liquid crystal display device 32, the first direction D1
corresponds to a vertical Y-direction and the second direction D2
corresponds to a horizontal X-direction. Here, an effective size ES1 of
the liquid crystal display device 32 in the first vertical direction D1
of the liquid crystal display device 32 is smaller than an effective size
ES2 of the liquid crystal display device 32 in the second horizontal
direction D2 (refer to FIG. 2B or the like). That is, a display region DA
of the liquid crystal display device 32 has a horizontally long shape.

[0040] The projective optical system 12 includes three lens groups L1 to
L3, and these lens groups L1 to L3 are supported in a lens-barrel 12a.
The lens-barrel 12a is accommodated in the casing 141 in FIG. 1. Each of
the lens groups L1 to L3 supported by the lens-barrel 12a is formed by
the composition of a plurality of lenses formed of a resin, in which a
size in the first direction D1 orthogonal to the first optical axis AX1
and a size in the second direction D2 are different from each other.
However, an optical surface of each of the lenses making up each of lens
groups L1 to L3 has a spherical surface shape or a non-spherical surface
that is rotationally symmetrical about the first optical axis AX1, and
there is no specific difference in a focusing property in the first
direction D1 and in the second direction D2. As shown in FIG. 3, an
optical surface 12f of the lens group L3 is exposed to an emission
opening EA, which is closest to a light emission side, of the lens-barrel
12a accommodating the lens groups L1 to L3. Here, an emission opening
width E1 of the emission opening EA in the first direction D1 is larger
than an emission opening width E2 of the emission opening EA in the
second direction D2 (refer to FIG. 2B or the like). That is, the emission
opening EA of the projective optical system 12 has a vertically long
shape. This is because as described later, in regard to the first
vertical direction D1, that is, in the Y-direction, it is possible to
make the image light GL be incident to the light guiding device 20 even
when the light GL has a relatively wide light beam width, but in regard
to the second horizontal direction D2, it is difficult to make the image
light GL be incident to the light guiding device 20 if the image light GL
does not have a relatively narrow light beam width.

[0041] The light guiding device 20 is formed by bonding the light guiding
member 21 and a light transmitting member 23, and makes up an optical
member having a flat plate shape that extends in parallel with an XY
plane, as a whole.

[0042] In the light guiding device 20, the light guiding member 21 is a
trapezoidal prism-shaped member in a plan view, has a first reflective
surface 21a, a second reflective surface 21b, a third reflective surface
21c, and a fourth reflective surface 21d as a side surface. In addition,
the light guiding member 21 has a top surface 21e and a bottom surface
21f that are adjacent to the first, second, third, and fourth reflective
surfaces 21a, 21b, 21e, and 21d, and are opposite to each other. Here,
the first and second reflective surfaces 21a and 21b extend along the XY
plane and are separated from each other by a thickness t of the light
guiding member 21. In addition, the third reflective surface 21c is
inclined at an acute angle α of 45° or less with respect to
the XY plane, and the fourth reflective surface 21d is inclined, for
example, at an acute angle β of 45° or less with respect to
the XY plane. The first optical axis AX1 passing through the third
reflective surface 21c and a second optical axis AX2 passing through the
fourth reflective surface 21d are disposed in parallel with each other
and are separated from each other by a distance D. In addition, as will
be described later in detail, a corner is removed and thereby an end
surface 21h is formed between the first reflective surface 21a and the
third reflective surface 21c. In addition, a corner is removed and
thereby an end surface 21i is formed between the first reflective surface
21a and the fourth reflective surface 21d. When including these end
surfaces 21h and 21i, the light guiding member 21 has an external form of
a polyhedral shape with eight faces.

[0043] The light guiding member 21 performs light guiding using a total
reflection by the first and second reflective surfaces 21a and 21b. There
are two directions, that is, a direction that is turned back by the
reflection at the time of light-guiding, and a direction that is not
turned back by the reflection at the time of light-guiding. When it is
considered in relation to an image guided by the light guiding member 21,
a horizontal direction that is turned back by plural times of reflection
at the time of light-guiding, that is, a confinement direction
corresponds to the second direction D2 of the liquid crystal display
device 32 when an optical path is developed to the light source side
perpendicular to the first and second reflective surfaces 21a and 21b (in
parallel with the Z-axis) as described later, a vertical direction that
is not turned back by the reflection at the time of light-guiding, that
is, a free propagation direction corresponds to the first direction D1 of
the liquid crystal display device 32 when an optical path is developed to
the light source side in parallel with the first and second reflective
surfaces 21a and 21b, and the third reflective surface 21c (in parallel
with the Y-axis) as described later.

[0044] The light guiding member 21 is formed of a resin material showing a
high light transmitting property at a visible range. The light guiding
member 21 is a member of a block state, which is integrally molded by
injection molding, and is formed, for example, by injecting a thermal
polymerization-type resin material into a metal mold and by thermally
curing this molded resin material. In this way, the light guiding member
21 is an integrally formed product, but functionally, may be considered
as being classified into a light incidence portion B1, a light guiding
portion B2, and a light emission portion B3.

[0045] The light incidence portion B1 is a triangular prism-shaped portion
and has a light incidence surface IS that is a part of the first
reflective surface 21a, and the third reflective surface 21c opposite to
the light incidence surface IS. The light incidence surface IS is a
rear-side or observer-side plane for taking in image light GL from the
image forming device 10, and extends in a direction orthogonal to the
first optical axis AX1 and opposite to the projective optical system 12.
The third reflective surface 21c is a rectangular total reflection mirror
that reflects the image light GL passed through the light incidence
surface IS and guides this reflected image light GL into the light
guiding portion B2.

[0046]FIG. 4A is a diagram illustrating the third reflective surface 21c,
and is a partially enlarged cross-sectional view of a surface portion P1
in the light incidence portion B1. The third reflective surface 21c has a
mirror layer 25 and is coated with a protective layer 26. This mirror
layer 25 is a total reflection coating and is formed by forming a film
through a vapor deposition of aluminum or the like on an inclined surface
RS of the light guiding member 21. The third reflective surface 21c is
inclined with respect to the first optical axis AX1 of the projective
optical system 12 or the XY plane, for example, at an acute angle α
of 25° to 27°, and turns back the image light GL that is
incident from the light incidence surface IS and faces a positive
Z-direction as a whole, in order for the image light GL to face a
negative X-direction close to a negative Z-direction as a whole, such
that the image light GL may be reliably guided into the light guiding
portion B2.

[0047] Returning to FIG. 2A or the like, the third reflective surface 21c
is a substantially rectangular plane. Here, an effective opening width F1
of the third reflective surface 21c in the first vertical direction D1 is
substantially the same as the emission opening width E1 of the projective
optical system 12 in the first direction D1. On the other hand, an
effective opening width F2 of the third reflective surface 21c in the
second horizontal direction (confinement direction) D2 is smaller than
the emission opening width E2 of the projective optical system 12 in the
second direction (confinement direction) D2. That is, in the projective
optical system 12, the horizontal emission opening width E2 is made to be
larger than the opening width F2 of the third reflective surface 21c, and
thereby the image light GL is made to be incident to the peripheral
portion of the third reflective surface 21c in the X-direction. In a
specific example, the opening width F2 of the third reflective surface
21c in the X-direction is set to, for example, substantially 18 mm. In
addition, in a specific example, the emission opening width E2 of the
projective optical system 12 in the X-direction is set to, for example,
substantially 19 mm or more. Here, as shown in FIG. 28, in the emission
opening EA of the projective optical system 12, an edge EG1 of the
negative X side, which is close to the light guiding portion B2, is
relatively more distant from a boundary BA between the third reflective
surface 21c and the second reflective surface 21b, and an edge EG2 of the
positive X side in the emission opening EA, which is distant from the
light guiding portion B2, is relatively less distant from an end surface
21h provided at a boundary between the third reflective surface 21c and
the first reflective surface 21a. This is considered to make the image
light GL sufficiently incident to the periphery of a boundary BA because
this boundary BA is distant from the projective optical system 12 in
relation to the end surface 21h.

[0048] In addition, a distance GA from the optical surface 12f of the lens
group L3, which is closest to the light emission side, of the projective
optical system 12 to the light incidence surface IS of the light
incidence portion B1 or the first reflective surface 21a is set to, for
example, 3 mm or less. In this way, when the projective optical system 12
is made to be close to the light incidence surface IS, it is possible to
effectively make the image light GL, which is emitted from the lens group
L3 that is closest to the light emission side of the projective optical
system 12, incident to the second reflective surface 21b.

[0049] The light guiding portion B2 has the first reflective surface 21a
and the second reflective surface 21b, which totally reflect the image
light turned back by the light incidence portion B1, as two planes that
extend in parallel with the XY plane and opposite to each other. A
distance between the first and second reflective surfaces 21a and 21b,
that is, a thickness t of the light guiding member 21 is set to, for
example, substantially 9 mm. Here, it is assumed that the first
reflective surface 21a is at a rear side or an observer side that is
close to the image forming device 10, and the second reflective surface
21b is at a front side or external side that is distant from the image
forming device 10. In this case, the first reflective surface 21a is a
plane portion that is common to the light incidence surface IS described
above or a light emission surface OS described later. The first and
second reflective surfaces 21a and 21b are total reflection surfaces
using a difference in refraction indexes, and to which a reflective coat
such as a mirror layer is not provided.

[0050]FIG. 4B is a diagram illustrating the first reflective surface 21a,
and is a partially enlarged cross-sectional view of a surface portion P2
in the light guiding portion B2 of the light guiding member 21. In
addition, FIG. 4c is a diagram illustrating the first reflective surface
21b, and is a partially enlarged crass-sectional view of the surface
portion P3 in the light guiding portion B2 of the light guiding member
21. The first and second reflective surfaces 21a and 21b are coated with
a hard coat layer 27 to prevent surface damage and thereby to prevent
deterioration in the resolution of a video. This hard coat layer 27 is
formed by forming a film through a dipping process or a spray coating
process of an UV-curable resin, a thermosetting resin, or the like on a
flat surface FS of the light guiding member 21. The image light GL
reflected by the third reflective surface 21c of the light incidence
portion B1 is, first, incident to the first reflective surface 21a and is
totally reflected. Next, the image light GL is incident to the second
reflective surface 21b and is totally reflected. Hereinafter, these
operations are repeated, and thereby the image light is guided to an
internal side of the light guiding device 20, that is, a negative X side
in which the light emission portion B3 is provided. In addition, a
reflective coat is not provided to the first and second reflective
surfaces 21a and 21b, such that external light that is incident to the
second reflective surface 21b from the external side passes through the
light guiding portion B2 with a high transmittance. That is, the light
guiding portion B2 is formed of a see-through type in which transparency
of an external image is possible.

[0051] The above-described total reflection at the first and second
reflective surfaces 21a and 21b may be made to occur at an inner side of
a surface SS of the hard coat layer 27 through a setting of a refractive
index of the hard coat layer 27, but may be made to occur at an inner
side of the flat surface FS.

[0052] Returning to FIG. 2A or the like, the light emission portion B3 is
a triangular prism-shaped portion, and has a light emission surface OS
that is a part of the first reflective surface 21a and the fourth
reflective surface 21d that is opposite to the light emission surface OS.
The light emission surface OS is a rear-side plane that emits the image
light GL to the observer's eye EY, and is formed of a part of the first
reflective surface 21a similarly to the light incidence surface IS, and
extends in a direction orthogonal to the second optical axis AX2. A
distance D between the second optical axis AX2 passing through the light
emission portion B3 and the first optical axis AX1 passing through the
light incidence portion B1 is set to, for example, 50 mm in consideration
of the width of the observer's head, or the like. The fourth reflective
surface 21d is a rectangular flat surface that reflects the image light
GL, which is incident through the first and second reflective surfaces
21a and 21b, and emits this image light GL to the outside of the light
emission portion B3. A half mirror layer 28 is attached to the fourth
reflective surface 21d. This half mirror layer 28 is a reflective film
having a light transmitting property (that is, a semi-transmissive
reflective film), and a surface thereof serves as a semi-transmissive
reflective surface. The half mirror layer (light-transmitting reflective
film) 28 is formed by forming a metallic reflective film or a dielectric
multi-layer film on the inclined surface RS of the light guiding member
21. Reflectance of the half mirror layer 28 with respect to the image
light GL is set to 10% to 50% within an assumed angle of incidence range
of the image light GL, from an aspect of making the observation of
external light GL' easy due to the see-through state. The reflectance of
the half mirror layer 28 with respect to the image light GL in a specific
example is set to, for example, 20%, and the transmittance with respect
to the image light GL is set to, for example, 80%.

[0053]FIG. 4D shows a diagram illustrating a structure of the fourth
reflective surface 21d and the periphery thereof, and which is
accompanied by an enlarged diagram of a cross-section of the half mirror
layer (light-transmitting reflective film) 28. As is clear from the
drawing, the half mirror layer (reflective film) 28 includes a metallic
reflective film 28a not having a polarization characteristic, a first
dielectric multi-layer film 28b having the polarization characteristic,
and a second dielectric multi-layer film 28c having the polarization
characteristic. Here, the metallic reflective film 28a is interposed
between the first dielectric multi-layer film 28b and the second
dielectric multi-layer film 28c. That is, the half mirror layer 28 has a
sandwich structure in which the metallic reflective film 28a is disposed
at the center. The metallic reflective film 28a is formed of, for
example, Ag film, Al film, or the like. The lower-side first dielectric
multi-layer film 28b or the upper-side second dielectric multi-layer film
28c is formed by laminating several layers or more of transparent
dielectric layers, and improves an angle characteristic or the like of
the metallic reflective film 28a. These dielectric multi-layer films 28b
and 28c may be omitted.

[0054] Returning to FIG. 2B or the like, the fourth reflective surface 21d
is inclined, for example, at an acute angle α of 25° to
27° with respect to the second optical axis AX2 or XY plane that
is orthogonal to the first reflective surface 21a, and the image light
GL, which is incident through the first and second reflective surfaces
21a and 21b of the light guiding portion B2, is partially reflected by
the half mirror layer 28 and is made to turn back to face the negative
Z-direction as a whole, and thereby the image light GL passes through the
light emission surface OS. In addition, the image light GL that is
transmitted through the fourth reflective surface 21d is incident to the
light transmitting member 23 and is not used for forming moving images.

[0055] A frame portion 29 includes a light transmitting portion 23, an
upper-side supporting member 24b, and a lower-side supporting member 24c.
Among these, a pair of the upper-side supporting member 24b and the
lower-side supporting member 24e is fixed to the light transmitting
member 23 while a left-side light guiding member 21 being vertically
interposed between the upper-side and lower-side supporting members 24b
and 24c. Through cooperation of these supporting members 24b and 24c, and
the light transmitting member 23, the light guiding member 21 is
positioned and fixed with respect to the light guiding member 23 not only
in the vertical Y-direction but also in the horizontal X-direction and
the back and forth Z-direction.

[0056] The light transmitting member 23 has the same refractive index as a
main body of the light guiding member 21, and has a first surface 23a, a
second surface 23b, and a third surface 23c. The first and second
surfaces 23a and 23b extend along the XY plane. In addition, the third
surface 23c is inclined with respect to the XY plane, and is disposed so
as to be opposite to the fourth reflective surface 21d of the light
guiding member 21 and in parallel therewith. That is, the light
transmitting member 23 is a member having a wedge-shaped member 23m that
is interposed between the second surface 23b and the third surface 23c.
The light transmitting member 23 is formed of a resin material showing a
high light transmitting property at a visible range similarly to the
light guiding member 21. The light transmitting member 23 is a member of
a block state, which is integrally molded by an injection molding, and is
formed, for example, by injecting a thermal polymerization-type resin
material into a metal mold and by thermally curing this molded resin
material.

[0057] In the light transmitting member 23, the first surface 23a is
disposed on an extended plane of the first reflective surface 21a
provided to the light guiding member 21 and is located at a rear side
close to the observer's eye EY, and the second surface 23b is disposed on
an extended plane of the second reflective surface 21b provided to the
light guiding member 21 and is located at a front side distant from the
observer's eye EY. The third surface 23c is a rectangular transmissive
surface that is bonded to the fourth reflective surface 21d of the light
guiding member 21 by an adhesive. An angle made by the first surface 23a
and the third surface 23c is the same as an angle c made by the second
reflective surface 21b and the fourth reflective surface 21d of the light
guiding member 21, and an angle made by the second surface 23b and the
third surface 23c is the same as an angle β made by the first
reflective surface 21a and the third reflective surface 21c of the light
guiding member 21.

[0058] The light transmitting member 23 and the light guiding member 21
make up a see-through portion B4 at a bonding portion of these members
and in the vicinity of the bonding portion and at a portion opposite to
the observer's eye. A wedge-shaped member 23m, which is interposed
between the second surface 23b and the third surface 23e making an acute
angle each other in the light transmitting member 23 and extends in the
negative X-direction, is bonded to the wedge-shaped light emission
portion B3 and thereby makes up a central portion in the X-direction in
the plate-shaped see-through portion B4 as a whole. A reflective coat
such as a mirror layer is not provided to the first and second surfaces
23a and 23b, such that these surfaces transmit the external light GL'
with a high transmittance similarly to the light guiding portion B2 of
the light guiding member 21. The third surface 23c may also transmit the
external light GL' with a high transmittance, but the fourth reflective
surface 21d of the light guiding member 21 is provided with the half
mirror layer 28, such that the external light GL' after passing through
the third surface 23c is reduced, for example, by 20%. That is, an
observer observes light in which the image light GL reduced to 20% and
the external light GL' reduced to 80% overlap each other.

[0059] Connecting portions 24e and 24f, which are provided to an end
portion of the upper-side supporting member 24b and the lower-side
supporting member 24c, respectively, are used to fix the lens-barrel 12a
of the projective optical system 12 to the frame portion 29, but also are
used for the attachment of the casing 141 in FIG. 1.

C. Outline of Optical Path of Image Light

[0060]FIG. 5A shows a diagram illustrating an optical path in the first
direction D1 corresponding to a vertical cross-section CS1 of the liquid
crystal display device 32. In the vertical cross-section along the first
direction D1, that is, a YZ plane (a Y'Z' plane after being developed),
in the image light emitted from the liquid crystal display device 32, a
component, which is emitted from an upper end side (a positive Y side) of
a display region 32b, indicated by a one-dotted line in the drawing is
set as an image light beam GLa, and a component, which is emitted from a
lower end side (a negative Y side) of a display region 32b, indicated by
a two-dotted line in the drawing is set as an image light beam GLb.

[0061] The upper-side image light beam GLa is converted into a parallel
light beam by the projective optical system 12, passes through the light
incidence portion B1, the light guiding portion B2, and the light
emission portion B3 of the light guiding member 21 along the developed
optical axis AX', and is incident to the observer's eye EY from an upper
side direction inclined at an angle of φ1, in a parallel light
beam state with respect to the observer's eye EY. On the other hand, the
lower-side image light beam GLb is converted into a parallel light beam
by the projective optical system 12, passes through the light incidence
portion B1, the light guiding portion B2, and the light emission portion
83 of the light guiding member 21 along the developed optical axis AX',
and is incident to the observer's eye EY from a lower side direction
inclined at an angle of φ2 (|φ2|=|φ1|) in a
parallel light beam state with respect to the observer's eye EY. The
angles φ1 and φ2 correspond to an upper half angle of
view and a lower half angle of view, respectively, and are set to, for
example, 6.5°.

[0062]FIG. 5B shows a diagram illustrating an optical path in the second
direction (confinement direction) D2 corresponding to a horizontal
cross-section CS2 of the liquid crystal display device 32. In the
horizontal cross-section along the second direction (confinement
direction or composite direction) D2, that is, an XZ plane (an X'Z' plane
after being developed), in the image light emitted from the liquid
crystal display device 32, a component, which is emitted from a first
display point P1 of a right end side (a positive X side) toward the
display region 32b, indicated by a one-dotted line in the drawing is set
as an image light beam GLc, and a component, which is emitted from a
second display point P2 of a left end side (a negative X side) toward the
display region 32b, indicated by a two-dotted line in the drawing is set
as an image light beam GLd. In FIG. 5B, an image light beam GLe emitted
from a right inner side and an image light beam GLf emitted from a left
inner side are added for reference.

[0063] The image light beam GLc from the right-side first display point P1
is converted into a parallel light beam by the projective optical system
12, passes through the light incidence portion B1, the light guiding
portion B2, and the light emission portion B3 of the light guiding member
21 along the developed optical axis AX', and is incident to the
observer's eye EY from a right side direction inclined at an angle of
θ1 in a parallel light beam state with respect to the
observer's eye EY. On the other hand, the image light GLd from the
left-side second display point P2 is converted into a parallel light beam
by the projective optical system 12, passes through the light incidence
portion B1, the light guiding portion B2, and the light emission portion
B3 of the light guiding member 21 along the developed optical axis AK,
and is incident to the observer's eye EY from a left-side direction
inclined at an angle of θ2 (|θ2|=|θ1|)
in a parallel light beam state with respect to the observer's eye EY. The
angles θ1 and θ2 correspond to a left half angle of
view and a right half angle of view, respectively, and are set to, for
example, 10°.

[0064] In addition, in regard to the horizontal direction, that is, the
second direction D2, the image light beams GLc and GLd are turned back by
reflection inside the light guiding member 21 and the number of times of
reflection of the image light beams GLc and GLd is different in each
case, such that each of the image light beams GLc and GLd is
discontinuously expressed in the light guiding member 21. In addition, in
regard to the observer's eye EY, a viewing direction is vertically
inverted compared to the case of FIG. 2A. Consequently, in regard to the
horizontal direction, a screen is horizontally inverted as a whole, but
as described later in detail, when the light guiding member 21 is
processed with high accuracy, a right half image of the liquid crystal
display device 32 and a left half image of the liquid crystal display
device 32 are continuously combined without a gap or deviation. In
addition, in consideration of the difference in the number of times of
reflection of the image light beams GLc and GLd inside the light guiding
member 21, the angle of emission θ1' of the right-side image
light beam GLc and the angle of emission θ2' of the left-side
image light beam GLd are made to be different from each other.

[0065] As described above, the image light beams GLa, GLb, GLc, and GLd
that are incident to the observer's eye EY become virtual images from
infinite distance, such that in regard to the first vertical direction
D1, moving images farmed on the liquid crystal display device 32 are made
to stand up, and in regard to the second horizontal direction D2, moving
images formed on the liquid crystal display device 32 are inverted.

D. Optical Path of Image Light in Relation to Horizontal Direction

[0066]FIG. 6 shows a cross-sectional view illustrating a specific optical
path in the first display device 100A. The projective optical system 12
includes three lenses L1, L2, and L3.

[0067] When passing through the lenses L1, L2, and L3 of the projective
optical system 12, image light beams GL11 and GL12 from the right-side
first display point P1 of the liquid crystal display device 32 are
converted into parallel light beams, and are incident to the light
incidence surface IS of the light guiding member 21. The image light
beams GL11 and GL12 guided to the inside of the light guiding member 21
repeat a total reflection on the first and second reflective surfaces 21a
and 21b at the same angle, and are eventually emitted from the light
emission surface OS as a parallel light beam. Specifically, the image
light beams GL11 and GL12 are reflected by the third reflective surface
21c of the light guiding member 21 as a parallel light beam, and then are
incident to the first reflective surface 21a of the light guiding member
21 at a first reflection angle γ1 and are totally reflected (total
reflection of a first time). Then, the image light beams GL11 and GL12
are incident to the second reflective surface 21b while maintaining the
first reflection angle γ1 and are totally reflected (total
reflection of a second time), and then are incident to the first
reflective surface 21a again and are totally reflected (total reflection
of a third time). As a result, the image light beams GL11 and GL12 repeat
the total reflection on the first and second reflective surfaces 21a and
21b while maintaining the first reflection angle γ1. The image
light beams GL11 and GL12 are totally reflected by the first and second
reflective surfaces 21a and 21b three times in total, and are incident to
the fourth reflective surface 21d. The image light beams GL11 and GL12
are reflected by the fourth reflective surface 21d at the same angle as
the third reflective surface 21c and are emitted from the light emission
surface OS as a parallel light beam at an inclination of an angle
θ1 with respect to the second optical axis AX2 direction that
is orthogonal to the light emission surface OS.

[0068] When passing through the lenses L1, L2, and L3 of the projective
optical system 12, image light beams GL21 and GL22 from the left-side
second display point P2 of the liquid crystal display device 32 are
converted into parallel light beams, and are incident to the light
incidence surface IS of the light guiding member 21. The image light
beams GL21 and GL22 guided to the inside of the light guiding member 21
repeat a total reflection on the first and second reflective surfaces 21a
and 21b at the same angle, and are eventually emitted from the light
emission surface OS as a parallel light beam. Specifically, the image
light beams GL21 and GL22 are reflected by the third reflective surface
21c of the light guiding member 21 as a parallel light beam, and then are
incident to the first reflective surface 21a of the light guiding member
21 at a second reflection angle γ2 (γ2<γ1) and are
totally reflected (total reflection of a first time). Then, the image
light beams GL21 and GL22 are incident to the second reflective surface
21b while maintaining the second reflection angle γ2 and are
totally reflected (total reflection of a second time), are incident again
to the first reflective surface 21a and are totally reflected (total
reflection of a third time), are incident again to the second reflective
surface 21b and are totally reflected (total reflection of a fourth
time), and are incident again to the first reflective surface 21a and are
totally reflected (total reflection of a fifth time). As a result, the
image light beams GL21 and GL22 are totally reflected by the first and
second reflective surfaces 21a and 21b five times in total and are
incident to the fourth reflective surface 21d. The image light beams GL21
and GL22 are reflected by the fourth reflective surface 21d at the same
angle as the third reflective surface 21c and are emitted from the light
emission surface OS as a parallel light beam at an inclination of an
angle θ2 with respect to the second optical axis AX2 direction
that is orthogonal to the light emission surface OS.

[0069] In FIG. 6, a first virtual surface 121a corresponding to the first
reflective surface 21a in a case where the light guiding member 21 is
developed, and a second virtual surface 121b corresponding to the second
reflective surface 21b in a case where the light guiding member 21 is
developed are illustrated. Through such a development, it can be seen
that the image light beams GL11 and GL12 from the first display point P1
pass through an incident equivalent surface IS' corresponding to the
light incidence surface IS, pass through the first surface 121a two
times, pass through the second surface 121b one time, are emitted from
the light emission surface OS, and are incident to the observer's eye EY.
In addition, it can be seen that the image light beams GL21 and GL22 from
the second display point P2 pass through an incidence equivalent surface
IS'' corresponding to the light incidence surface IS, pass through the
first surface 121a three times, pass through the second surface 121b two
times, are emitted from the light emission surface OS, and are incident
to the observer's eye EY. In other words, the observer observes the lens
L3 of the projective optical system 12 that is present in the vicinity of
the two incidence equivalent surfaces IS' and IS that are present at
positions different from each other in an overlapped manner.

[0070]FIG. 7A shows a diagram conceptionally illustrating a display
surface of a liquid crystal display device 32, FIG. 7B is a diagram
conceptionally illustrating a virtual image of the liquid crystal display
device 32, which is viewed by an observer, and FIGS. 7C and 7D are
diagrams illustrating partial images making up the virtual image. A
rectangular image forming region AD provided to the liquid crystal
display device 32 shown in FIG. 7A is observed as a virtual image display
region AI shown in FIG. 7B. A first projection image IM1 corresponding to
a portion ranging from center to right-side in the image forming region
AD of the liquid crystal display device 32 is formed at a left-side of
the virtual image display region AI, and this first projection image IM1
becomes a partial image in which a right-side is deficient as shown in
FIG. 7C. In addition, a second projection image IM2 corresponding to a
portion ranging from center to left-side in the image forming region AD
of the liquid crystal display device 32 is formed as a virtual image at a
right-side of the virtual image display region A1, and this second
projection image IM2 becomes a partial image in which a left-side is
deficient as shown in FIG. 7D.

[0071] A first partial region A10, which forms only the first projection
image (virtual image) IM1 in the liquid crystal display device 32 shown
in FIG. 7A, includes, for example, the first display point P1 of the
right end of the liquid crystal display device 32 and emits the image
light beams GL11 and GL12 that are totally reflected in the light guiding
portion B2 of the light, guiding member 21 three times in total. A second
partial region A20, which forms only the second projection image (virtual
image) IM2 in the liquid crystal display device 32 includes, for example,
the second display point P2 of the left end of the liquid crystal display
device 32 and emits the image light beams GL21 and GL22 that are totally
reflected in the light guiding portion B2 of the light guiding member 21
five times in total. Image light from a band SA near the center of the
image forming region AD of the liquid crystal display device 32, which is
interposed between the first and second partial regions A10 and A20 and
extends vertically, forms a superimposed image SI shown in FIG. 7B. That
is, image light from the band SA of the liquid crystal display device 32
includes the first projection image IM1 formed by the image light beams
GL11 and GL12 that are totally reflected in the light guiding portion B2
three times in total, and the second projection image IM2 formed by the
image light beams GL21 and GL22 that are totally reflected in the light
guiding portion B2 five times in total, and these first and second
projection images IM1 and IM2 overlap each other on the virtual image
display region AI. When the light guiding member 21 is accurately
processed, and thereby a light beam that is accurately collimated by the
projective optical system 12 is formed, it is possible to prevent
deviation or bleeding due to overlapping of the two projection images IM1
and IM2 with respect to the superimposed image SI.

E. Prevention of Deterioration of Image

[0072] Hereinafter, deterioration of an image in a superimposed image SI
shown in FIG. 7B or the like will be described. The superimposed image SI
may be considered as an image formed in such a manner that a peripheral
part of the first projective image IM1 shown in FIG. 7C and a peripheral
part of the second projective image IM2 shown in FIG. 7D are
superimposed, and in a case where an angle of view of the projective
optical system 12 is small, partial light shielding called shading is
generated at the periphery. In the case of the image forming device 10 of
this embodiment, even when the center of the image forming region AD is
formed of the superimposed image SI and the addition of an amount of
light is present, reduction in brightness may easily occur in the center
due to a peripheral light reduction of the first and second projective
images IM1 and IM2. In addition, in the case of the image forming device
10 of this embodiment, the image light GL making up the superimposed
image SI has a high tendency of being emitted from both end portions in
the second direction D2 in the emission opening EA of the projective
optical system 12.

[0073]FIG. 8 shows a diagram illustrating the reason why the image light
GL making up the superimposed image SI has the high tendency of being
emitted from both end portions in the second direction D2 in the emission
opening EA of the projective optical system 12. In regard to a horizontal
cross-section along the second direction (confinement direction) D2, in
image light emitted from a center of the liquid crystal display device
32, components inclined to a positive X side, which are indicated by a
one-dotted line in the drawing, are set as image light beams GL31 and
GL32, and in the image light emitted from the center of the liquid
crystal display device 32, components inclined to a negative X side,
which are indicated by a one-dotted line in the drawing, are set as image
light beams GL41 and GL42. The former image light beams GL31 and GL32 are
incident to a left-side of the eye EY as a parallel light beam that is
parallel with the second optical axis AX2, and the latter image light
beams GL41 and GL42 are incident to a right-side of the eye EY as a
parallel light beams that is parallel with the second optical axis AX2.
These image light beams GL31, GL32, GL41, and GL42, and more
particularly, the image light beams GL32 and GL42 with a large angle of
inclination pass through an external side of the projective optical
system 12, and are incident to positions near the boundary BA and the end
surface 21h in the third reflective surface 21c provided to the light
incidence portion B1 of the light guiding member 21. Therefore, the width
of projective optical system 12, and more particularly, the lens group L3
in the second direction (confinement direction) D2 is made to be
sufficiently large so as to sufficiently cover the third reflective
surface 21c, and thereby the image light GL is made to be efficiently
incident to the light guiding device 20. That is, as shown in FIG. 2B or
the like, the emission opening width E2 of the projective optical system
12 in the second direction (confinement direction) D2 is made to be
larger than the opening width F2 of the third reflective surface 21c to
prevent the deficiency of the image light from occurring. In addition, in
a case where the emission opening width E2 of the projective optical
system 12 in the second direction (confinement direction) D2 is smaller
than the opening width F2 of the third reflective surface 21c, the
deficiency of the center-side light beams such as the image light beams
GL32 and GL42 with a large angle of inclination becomes significant, such
that deterioration such as the occurrence of deficiency of the image in
the vicinity of the horizontally center portion of the image or the
significant reduction in light in the vicinity of the horizontally center
portion of the image may occur.

[0074] In addition, the above-described phenomenon may be generally
canceled out when the width of the second direction D2 (confinement
direction) of the projective optical system 12 is made to have
substantially the same width as the first direction D1. However, in a
head-mounted display of an eyeglasses-type like this embodiment, weight
reduction is important, such that it is preferable that the width of the
projective optical system 12 in the second direction (confinement
direction) D2 be shortened as possible. As a result, it is preferable
that the emission opening width E2 of the projective optical system 12 in
the X-direction be equal to or less than a value obtained by adding
several millimeters to the opening width F2 of the third reflective
surface 21c in the X-direction.

[0075] In addition, a horizontal width or an overlapping width of the band
SA in FIG. 7B where the overlapping occurs may be adjusted by controlling
an angle range of the illumination light SL that illuminates the liquid
crystal display device 32. In this embodiment, the angle range of the
illumination light SL is not particularly adjusted, such that the band SA
of the horizontal width or the overlapping width that corresponds to a
divergence characteristic of the backlight light-guiding portion 31b or
the like is present.

[0076] Hereinbefore, the number of times of total reflection of the image
light beams GL11 and GL12 emitted from the first partial region A10
including the first display point P1 of the right-side of the liquid
crystal display device 32 by the first and second reflective surfaces 21a
and 21b is set to three times in total, and the number of times of total
reflection of the image light beams GL21 and 22 emitted from the second
partial region A20 including the second display point P2 of the left-side
of the liquid crystal display device 32 by the first and second
reflective surfaces 21a and 21b is set to five times in total, but the
number of times of total reflection may be appropriately changed. That
is, through an adjustment of external form (that is, the thickness t, the
distance D, and acute angles c and 3) of the light guiding member 21, the
number of times of total reflection of the image light beams GL11 and
GL12 may be set to five times in total, and the number of times of total
reflection of the image light beams GL21 and GL22 may be set to seven
times in total. In addition, hereinbefore, the number of times of total
reflection of the image light beams GL11, GL12, GL21, and GL22 is an odd
number, but when the light incidence surface IS and the light emission
surface OS are disposed at an opposite side, that is, the light guiding
member 21 is made to have a parallelogram shape in a plan view, the
number of times of total reflection of the image light beams GL11, GL12,
GL21, and GL22 becomes an even number.

F. Processing of Ghost Light

[0077]FIG. 9A shows an enlarged diagram illustrating the reason why a
first end surface 21h formed by removing a corner is provided to the
light guiding member 21 shown in FIG. 2A or the like. The image light GL
incident to a position near a corner 121h of the light guiding member 21
is reflected by the third reflective surface 21c and then is reflected by
the first reflective surface 21a, but the image light GL is reflected by
the first reflective surface 21a and then is reflected again by the third
reflective surface 21c. The unnecessary light HL as such re-reflected
light is not parallel to the original image light GL due to the
reflection at the third reflective surface 21c and is guided to an
unforeseen optical path, and thereby a part thereof may be guided to the
light emission portion B3 and may be emitted from the light emission
surface OS. That is, the unnecessary light HL generated at the corner
121h becomes the ghost light GG that is not preferable, such that it is
preferable to remove the unnecessary light HL in advance. Therefore, the
corner 121h is removed to provide an end surface 21h that blocks stray
light, thereby imposing restrictions on the optical path of the
unnecessary light HL.

[0078]FIG. 9B shows an enlarged diagram illustrating the reason why the
second end surface 21i that is formed by removing a corner is provided to
the light guiding member 21 shown in FIG. 2A or the like. In this case,
the end surface 21i is provided by removing a corner 121i at the fourth
reflective surface 21d side of the light guiding member 21. A coat or a
roughened surface with, for example, a relatively high reflectance is
formed on the end surface 21i, and a step difference that is fitted to
the end surface 21i is also provided to the light transmitting member 23.
By providing such an end surface 21i, it is possible to prevent the
unnecessary light HL, which occurs in a case where the normal image light
GL propagated through the light guiding member 21 is reflected by the
fourth reflective surface 21d two times or more, or the unnecessary light
HL, which occurs in a case where the normal image light GL passes through
the light guiding portion B2 by being reflected less than three times and
is reflected by the fourth reflective surface 21d, from being emitted to
the outside through the light emission surface OS. That is, the end
surface 21i prevents the unnecessary light HL, which is inclined with
respect to the original image light GL after passing through a path other
than an assumed path, from being the ghost light GG that is not
preferable.

G. Others

[0079]FIG. 10A shows a diagram illustrating a modification of the light
guiding member 21 shown in FIG. 2A or the like. In the above description,
it is described that the image light that is propagated by the light
guiding member 21 is totally reflected with respect to the first and
second reflective surfaces 21a and 21b at only two reflection angles
γ1 and γ2, but similarly to the light guiding member 21 of
the modification shown in FIG. 10A, three components of image light GL31,
GL32, and GL33 may be permitted to be totally reflected at reflection
angles γ1, γ2, and γ3
(γ1>γ2>γ3), respectively. In this case, the image
light GL emitted from the liquid crystal display device 32 is propagated
in three modes, and is combined at a position of the observer's eye EY
and is perceived as a virtual image. In this case, as shown in FIG. 10B,
a projection image IM21 subjected to the total reflection, for example,
three times in total is formed at a left-side of the effective display
region A0, a projection image IM22 subjected to the total reflection, for
example, five times in total is formed near the center of the effective
display region A0, and a projection image IM23 subjected to the total
reflection, for example, seven times in total is formed at a right-side
of the effective display region A0.

[0080] In the above-described virtual image display device 100, the image
light GL reflected by the third reflective surface 21c of the light
incidence portion B1 is propagated while being totally reflected by the
first and second reflective surfaces 21a and 21b of the light guiding
portion, and is reflected by the fourth reflective surface 21d of the
light emission portion B3, and is incident to the observer's eye EY as a
virtual image. At this time, the number of times of reflection of the
first image light beams GL11 and GL12, which are emitted from the first
partial region A10 including the first display point P1 of the image
display device 11, at the light guiding portion, and the number of times
of reflection of the second image light beams GL21 and GL22, which are
emitted from the second partial region A20 including the second display
point P2 of the image display device 11, at the light guiding portion B2,
are different from each other, such that it is possible to take a wide
angle width of an angle of emission of the image light GL emitted from
the light emission portion B3. That is, it is possible to take in the
image light GL from the different partial regions A10 and A20 in the
image display device 11 at a relatively wide angle of view, such that it
is possible to secure a large display size of a virtual image that is
observed over the light emission portion B3. In this way, due to the
setting of a structure in which image light beams GL in which the number
of times of reflection is different are taken out, it is possible to make
the light emission portion B3 large so as to cover a pupil without making
the light guiding portion B2 too much thicker, and therefore it is not
necessary to perform a pupil division by making the light emission
portion B3 close to the pupil. As a result, it is possible to secure a
large Eyring diameter and thereby preferable see-through observation may
be realized.

[0081] In addition, in regard to the second direction (confinement
direction) D2 that is turned back by the reflection at the time of
light-guiding, the virtual image display device 100 of this embodiment
has the emission opening width E21 that is larger than the opening width
F2 of the third reflective surface 21c, such that it is possible to
prevent a partial deficiency of image light GL when the image light GL
emitted from the projective optical system 12 is incident to the third
reflective surface 21c from occurring, and thereby it is possible to
prevent the occurrence of deficiency of an image or a large variation in
brightness.

[0082] Hereinbefore, the invention is described based on the embodiment,
but the invention is not limited to the embodiment, and may be executed
with various aspects without departing from the scope of the invention.
For example, the following modifications may be made.

[0083] In the above-described embodiment, the reflectance of the half
mirror layer 28 provided on the fourth reflective surface 21d of the
light guiding member 21 is set to 20% and thereby priority is given to
the see-through state, but the reflectance of the half mirror layer 28 is
set to 50% or more and thereby priority may be given to the image light.
In addition, the half mirror layer 28 may not be formed on the entirety
of the fourth reflective surface 21d, and may be formed at a necessary
partial region. In addition, the half mirror layer 28 may be on the third
surface 23c of the light transmitting member 23.

[0084] A shape of the light transmitting member 23 is not limited to a
shape obtained by extending the light guiding member 21 in the horizontal
direction, that is, in the X-direction, and may include a portion that is
extended to vertically interpose the light guiding member 21.

[0085] In the above-described embodiment, the illumination light SL from
the illumination device 31 is made not to have a particular directivity,
but the illumination light SL may have a directivity according to a
position of the liquid crystal display device 32. According to this
configuration, it is possible to effectively illuminate the liquid
crystal display device 32 and thereby it is possible to reduce a
variation in brightness due to a position of the image light GL.

[0086] In the above-described embodiment, a display brightness of the
liquid crystal display device 32 is not particularly adjusted, but the
display brightness may be adjusted according to a range or a
superimposition of the projection images IM1 and IM2 as shown in FIG. 7B.

[0087] In the above-described embodiment, the transmission-type liquid
crystal display device 32 or the like is used as the image display device
11, but as the image display device 11, various devices may be used
without being limited to the transmission-type liquid crystal display
device 32. For example, a configuration using a reflective liquid crystal
display device is possible, and a digital micro mirror device or the like
may be used instead of the liquid crystal display device 32. In addition,
as the image display device 11, a self-luminescent device represented by
an LED array, an OLED (organic EL), or the like may be used.

[0088] The virtual image display device 100 of the above-described
embodiment is configured to have a pair of image forming device 10 and
light guiding device 20 in correspondence with each of a right eye and a
left eye, but the virtual image display device 100 may be configured to
have the image forming device 10 and the light guiding device 20 to
either the right eye or the left eye to view an image with one eye.

[0089] In the above-described embodiment, the first optical axis AX1
passing through the light incidence surface IS and the second optical
axis AX2 passing through the light incidence surface IS are parallel with
each other, but these optical axes AX1 and AX2 may be not parallel with
each other.

[0090] In the above description, the virtual image display device 100 is
specifically described as a head-mounted display, but the virtual image
display device 100 may be modified as a head-up display.

[0091] In the above description, in regard to the first and second
reflective surfaces 21a and 21b, image light is totally reflected by an
interface with air and is guided without forming a mirror, a half mirror,
or the like on the surface, but the total reflection in the invention
includes a reflection that occurs in a state where a mirror coat or a
half mirror film is formed on the entirety of the first and second
reflective surfaces 21a and 21b or a part thereof. For example, the total
reflection in the invention includes a case where an angle of incidence
of image light satisfies a total reflection condition, the mirror coat or
the like is formed on the entirety of the first and second reflective
surfaces 21a and 21b or a part thereof and thereby substantially all of
the image light beams are reflected. In addition, as long as sufficiently
bright image light is obtained, the entirety of the first and second
reflective surfaces 21a and 21b or a part thereof may be coated with a
more or less transmissive mirror.

[0092] In the above description, the light guiding member 21 extends in
the horizontal direction that is parallel with the eye EY, but the light
guiding member 21 may extend in the vertical direction. In this case, the
optical panel 110 has a parallel configuration in parallel not in series.